[PATCH] SCSI: run queue if SCSI device queue isn't ready and queue is idle

[Ming Lei <ming.lei@redhat.com>]

Before commit 0df21c86bdbf ("scsi: implement .get_budget and .put_budget
for blk-mq"), we run queue after 3ms if queue is idle and SCSI device
queue isn't ready, which is done in handling BLK_STS_RESOURCE. After
commit 0df21c86bdbf is introduced, queue won't be run any more under
this situation.

IO hang is observed when timeout happened, and this patch fixes the IO
hang issue by running queue after delay in scsi_dev_queue_ready, just like
non-mq. This issue can be triggered by the following script[1].

There is another issue which can be covered by running idle queue:
when .get_budget() is called on request coming from hctx->dispatch_list,
if one request just completes during .get_budget(), we can't depend on
SCSI's restart to make progress any more. This patch fixes the race too.

With this patch, we basically recover to previous behaviour(before commit
0df21c86bdbf) of handling idle queue when running out of resource.

[1] script for test/verify SCSI timeout
rmmod scsi_debug
modprobe scsi_debug max_queue=1

DEVICE=`ls -d /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/* | head -1 | xargs basename`
DISK_DIR=`ls -d /sys/block/$DEVICE/device/scsi_disk/*`

echo "using scsi device $DEVICE"
echo "-1" >/sys/bus/pseudo/drivers/scsi_debug/every_nth
echo "temporary write through" >$DISK_DIR/cache_type
echo "128" >/sys/bus/pseudo/drivers/scsi_debug/opts
echo none > /sys/block/$DEVICE/queue/scheduler
dd if=/dev/$DEVICE of=/dev/null bs=1M iflag=direct count=1 &
sleep 5
echo "0" >/sys/bus/pseudo/drivers/scsi_debug/opts
wait
echo "SUCCESS"

Fixes: 0df21c86bdbf ("scsi: implement .get_budget and .put_budget for blk-mq")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/scsi/scsi_lib.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index db9556662e27..1816dd8259b3 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1967,6 +1967,8 @@ static bool scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
 out_put_device:
 	put_device(&sdev->sdev_gendev);
 out:
+	if (atomic_read(&sdev->device_busy) == 0 && !scsi_device_blocked(sdev))
+		blk_mq_delay_run_hw_queue(hctx, SCSI_QUEUE_DELAY);
 	return false;
 }
 
-- 
2.9.5